1. Field of the Invention
The present invention relates to refrigeration systems and more particularly to refrigeration system status monitors operatively correlated with automatic controls.
2. Description of the Prior Art
Failure of commercial refrigeration and air conditioning systems often risks significant secondary financial losses. Insurance against unforseen loss due to refrigeration system malfunction or failure is commonly carried at substantial cost by businesses utilizing frozen and chilled food storage, frozen food retail displays, air conditioning for theaters, sales rooms, computer equipment facilities, and many other commercial and industrial operations adversely sensitive to conditions of excessive heat or humidity.
Refrigeration monitoring equipment presently exists which senses and indicates operational status of refrigeration systems at the time of or subsequent to equipment malfunction or failure. During night time hours and on weekends and holidays when attendants or when refrigeration maintenance service is not readily available, current status indicators are not adequate to prevent serious losses following refrigeration system breakdowns. The present invention is directed to provide advance warning of likely refrigeration system malfunction as well as current system status indicators.
Refrigeration system failure with minor exceptions, is due to one of three conditions. These are leakage into or out of the system, circulation malfunction or improper compressor lubricant oil conditions. Of these three causes of malfunction or failure, the last, inadequate compressor lubrication, is the most frequent and most often the cause of catastrophic system malfunction. Refrigeration compressor lubrication is unique in that the refrigerant fluid mixes with the lubricating oil and creates lubrication hazards not commonly encountered in other classes of high speed rotating machinery.
The present invention, directly or indirectly, senses system malfunction precursor conditions brought about by any one or combinations of the foregoing causes of failure.
The quantity of refrigerant in a typical commercial size system may be twenty or more times greater than the quantity of lubricating crankcase oil in the system compressor. Normally, a portion of the crankcase oil is carried around the refrigeration system by the refrigerant. However, if too much oil leaves the compressor crankcase, or if too much oil is suddenly returned with the refrigerant to the compressor through the compressor inlet, failure of the compressor may result.
Should the liquid refrigerant replace the oil in the compressor crankcase during an inversion of the oil and refrigerant, which may occur with certain commonly used refrigerants when a sufficiently low crankcase temperature is attained, the oil in the compressor will be very completely swept out of the compressor and all lubricated interaction of the moving parts and bearing surfaces of the compressor will quickly be lost. Rapid catastrophic failure of the compressor and of the system results.
The presence of air or moisture in the system mixed with the refrigerant reduces the cooling capacity of the system and overburdens the compressor and other system components. Air and moisture commonly enter into refrigeration systems through small leaks or are present from the time the system was last sealed. Such small leaks or residues of air or moisture are often not detected during routine maintenance inspection.
The presence of liquid refrigerant in the low pressure gas return line may result in the compressor inlet being filled with liquid refrigerant. Such a condition is often encountered during temporary shutdowns. If the compressor should then be started, immediate damage to the compressor and system failure is likely to result.
With only infrequently occurring exceptions, the above enumerated conditions underlying refrigeration system malfunctions and failures are characterized by gradually worsening precursor physical and thermodynamic conditions within the refrigeration system fluid mixtures. The compressor crankcase provides one convenient site for mounting sensors for the purpose of monitoring and detecting critical fluid mixture conditions characteristic of normal operation, as well as those fluid mixture conditions characteristic of precursor malfunction conditions.
The normal operating dynamic range of the sensible properties of refrigeration fluid mixtures, temperature, pressure, density, heat dissipation constants and others is very large. Static detection systems, which depend upon sensing a single parameter, accordingly, are of little use in discriminating between, on the one hand, normal and on the other hand, incipient precursor malfunction conditions. It is in sensing the changing relationships between physical properties within the refrigeration fluids, that precursor malfunction conditions may be readily detected.
Refrigeration malfunction causal factors frequently include an extreme temperature or thermodynamic property excursion of the refrigerant mixture. With the passage of time following the system malfunction but prior to the arrival of refrigeration service people, the refrigeration fluids may and often do change temperature, or thermodynamic state. Thus, the refrigeration service and repair work may be extremely baffling and time consuming to track down an intermittent and transitory cause of system malfunction. A means to record unusual conditions, even transitory phenomena occurring within the refrigerant mixtures would, if available, greatly aid diagnosis for maintenance service. Heretofore, refrigeration monitoring equipment, except for temperature recording of the freezer compartment itself, has failed to record operating status conditions within the system.